We have designed a study to detect molecular alterations (p53 mutations and amplifications of HER-2/neu and PRAD1) and protein expression products that may serve independently or jointly with histopathology to improve predictive capability for breast cancer. The study utilizes surgical specimens derived from a cohort of 6805 women who underwent biopsy for non-malignant breast disease at the Mayo Rochester-affiliated hospitals from January 1, 1967, to December 31, 1981. The cohort was followed until January l, 1987, during which time 236 cases of breast cancer occurred. Comparable women who did not develop breast cancer during the same interval have been selected as controls. The primary objectives of the study are: 1. To determine the frequency of p53 mutations and related immunohistochemical (IHC) markers in surgical specimens from women with benign breast disease. 2. To compare the pattern of p53 mutations (and related IHC markers) in paired benign and malignant tissues. 3. To determine whether the subsequent tumors that emerge from p53 positive women differ from p53 negative women in the profile of molecular mutations at p53, HER-2, and PRAD1, and in histologic appearance of the tumors. 4. To determine whether selected IHC markers in benign breast disease may define breast cancer risk. 5. To determine if the presence of these molecular lesions or IHC markers, in conjunction with histologic characteristics and epidemiologic risk factors, is predictive of eventual progression to breast cancer. Using novel laboratory techniques for detecting molecular lesions in minute quantities of DNA from formalin-fixed, paraffin-embedded sections, we are examining tissues from both benign and malignant lesions. Recent analyses have detected p53 mutations in 8% of the benign breast samples tested, but no evidence of gene amplification at the HER-2 and the PRAD1 loci. Our proposed study will complete the molecular analysis of benign breast tissue centering on p53 and consequences of p53 abnormalities to determine if these alterations predict the subsequent development of breast cancer. This study will provide information on the role of genetic and immunohistochemical markers in benign breast disease and will evaluate the utility of these markers in identifying women at high risk of breast cancer.